Ceramic dielectric materials of perovskite barium-lead sodium niobate

ABSTRACT

A CERAMIC MATERIAL IN A PEROVSKITE STRUCTURE HAVING A HIGH DIELECTRIC PERMITTIVITY, A LOW POWER FACTOR AND A LOW TEMPERATURE COEFFICENT OF PERMITTIVITY, THE COMPOSITION OF WHICH IS IN A CHEMICAL FORMULA OF   (BAXPB1-X) (NA0.25NB0.75)O3   WHEREIN X RANGES FROM 0.40 TO 0.95 IN ACCORDANCE WITH THE INVENTIONS. THE CERAMIC DIELECTRIC COMPOSITION OF   (BAXPB1-X) (NA0.25NB0.75)O3   CAN BE MODIFIED BY SUBSTITUTION OF SR FOR BA OR LI FOR NA IN ACCORDANCE WITH THE INVENTIONS.

Jan. 30, 1973 YOsHfl-"RQ rsuo ET AL 3,713,853

CERAMIC DIELECTRIC MATERIALS 01" PEROVSKI'I'U BARIUM-LEAD SODIUM NIOBATE Filed June 12, 1970 YOSHIHIRO MATSUO, HIROMU SASAKI, and SHIGERU HAYAKAWA, Inventors Attorneys United States Patent 3,713,853 CERAMIC DIELECTRIC MATERIALS 0F PEROV- SKITE BARIUM-LEAD SODIUM NIOBATE Yoshihiro Matsuo, 27-4 Ishizu Higashi-cho, Neyagawashi; Hiromu Sasaki, 546-39 Oaza Kamishimagashira, Kadoma-shi; and Shigeru Hayakawa, 7-16-13 Korigaoka, Hirakata-shi, all of Osaka, Japan Filed June 12, 1970, Ser. No. 45,869 Int. Cl. C04b 33/00 US. Cl. 10639.5 3 Claims ABSTRACT OF THE DISCLOSURE A ceramic material in a perovskite structure having a high dielectric permittivity, a low power factor and a low temperature coefficient of permittivity, the composition of which is in a chemical formula of x l-x) o.2s 0.75) 3 wherein x ranges from 0.40 to 0.95 in accordance with the inventions. The ceramic dielectric composition of can be modified by substitution of Sr for Ba or Li for Na in accordance with the inventions.

This invention relates to ceramic dielectric materials and more specially to ceramic dielectric materials in a perovskite structure. which have a high dielectric permittivity, a low power factor and a low temperature coefficient of permittivity.

Since the recent electronic industry has required miniaturization and refinement of electrical equipment, there is an increasing need for a dielectric material of a high permittivity, a low power factor and a low temperature coefiicient of permittivity. High permittivity facilitates producing a capacitor in a small physical size for a given capacitance and low power factor prevents a capacitor from being heated. Heat generation is a serious problem in miniaturized electrical equipment. Low temperature coefficient of permittivity of a capacitor enables electrical equipment or device to work in a high accuracy. It is also desired that the temperature coefiicient of permittivity can be chosen at a specific value.

Therefore, it is an object of the present invention to provide ceramic dielectric materials characterized by high permittivity, low power factor.

Another object of the present invention is to provide ceramic dielectric materials characterized by high permittivity, low power factor and a linear temperature coefficient of permittivity.

These and other objects will be apparent upon consideration of following detailed description taken together with accompanying drawing wherein:

The drawing illustrates a cross sectional view of a capacitor contemplated by the present invention.

Before proceeding with a detailed description of the nature of a capacitor embodying the invention, the construction of such a capacitor will be described with reference to the drawing. In this drawing, character 10 indicates generally a capacitor comprising a sintered disc 11 of dielectric material according to the invention. The sintered disc 11 is provided on two opposite surfaces with electrodes 12 and 13. The electrodes 12 and 13 may be applied to the surfaces by any suitable and available method, for example, by firing-on silver electrode paint commercially available. The disc 11 is a plate which may have any of suitable shapes, for example, circular, square or rectangular. Wire leads 15 and 16 are attached con- Patented Jan. 30 1973 ice wherein x ranges from 0.40 to 0.95 in accordance with the inventions.

A sintered disc having a composition of chemical Formula 1 is in a perovskite structure and has a permittivity of 200 to 450, a power factor lower than 10X 10- and a temperature coeificient of permittivity of -50 to -100 p.p.m./ C. If the x in chemical Formula 1 is out of the range of 0.40 to 0.95, the resultant disc does not show a power factor less than 10X l0 as shown in Table l.

The ceramic dielectric composition of chemical Formula 1 can be modified by substitution of Sr for Ba in accordance with the invention: the Sr-modified composition is represented by chemical Formula 2:

( x 1x) o.25 0.75) 3 wherein x ranges from 0.50 to 0.97 in accordance with the invention. A sintered disc having a composition of chemical Formula 2 is in a perovskite structure and has a permittivity of 90 to 390, a power factor lower than 10 10 and a temperature coefiicient of permittivity of to 1600 p.p.m./ C. If the x in chemical Formula 2 is outside of the range of 0.50 to 0.97, the resultant disc does not show a power factor less than 10x10, shown in Table 2.

The ceramic dielectric composition of chemical Formula 2 can be modified by substitution of Li for Na in accordance with the invention: The Li-modified composition is represented by chemical Formula 3:

( x 1x) azs oxza) s wherein x ranges from 0.5 to 0.97 in accordance with the invention. A sintered disc having the composition of chemical Formula 3 is in a perovskite structure and has a permittivity of 80 to 340, a power factor lower than 10X 10- and a temperature coefiicient of permittivity of -40 to -800 p.p.m./ C. If the x in chemical Formula 3 is outside of the range of 0.5 to 0.97, the resultant disc does not show a power factor less than 10 10'- as shown in Table 3.

The composition in chemical Formulae 1 to 3 can be prepared by mixtures of ingredient oxides in mole ratio dependent upon the chemical formulae. For example, the composition in chemical Formula 1 can be prepared by the following mixture listed in Table 4, wherein x ranges from 0.40 to 0.95. It is possible to employ, as the starting material, any compound which is converted into an oxide during firing process. Operable starting materials which may be employed in place of an oxide are, for example, carbonates, hydrooxides, and oxalates. A given mixture is Well mixed by a wet ball mill, dried, calcined, pulverized, and pressed into discs. The pressed discs are fired at a given temperature dependent upon compositions of mixtures. The Ag-electrode is attached to both surfaces of the fired disc. Permittivity and power factor of the discs are measured at a constant applied field of 1 mHz. as a function of temperature from --l to 300 C. The temperature coefiicient of permittivity (or) is usually defined by the following equation:

nt=e(80 C.)e(20 C.)/e(20 C.) (80 C.20 C.)

wherein 480 0. is a permittivity at 80 c. e(20 C.) is a permittivity at 20 C.

Example TABLE 4 Compositions corresponding to the chemical formulae gf i oxide (Bao) Moleyzano listed in column 1 of Table 5 are prepared by using start- Lead oxide (Pbb) ing materials of barium carbonate, strontium carbonate, Sodium oxide -6; 125 lead oxide, sodium carbonate, lithium carbonate, and nio- Niobium oxide O 0'375 bium oxide. The mixtures of starting materials in given 2 TABLE 5 Column 1 2 3 4 5 6 First Final Permit- Powerfac- Temperature firing firing tivity tor at 20 coefiicient temperatemperaat 20 C. C. and r of Sample ture ture and 1 mHz permittivity number Composition 0.) C.) 1 mHz (X- (p.p.m./ C.)

( eo.osPbo,os) 8.0.25N 130.75) 08 1, 250 1, 400 200 5 -50 (BamPbon) au.zsNbo.1a) 3 1, 200 1, 350 300 5 l0O ama m) fldb bflflfig a 1, 100 1, 300 350 5 300 (BBILGPbOA; (Nan.25Nbo.1s 03 1,000 1,200 450 7 -700 (Ban.4Pbo.e (Nao.25Nbo,75)Oa 900 1,000 450 10 -1,000 (SrwPbm) (N bo,7s)0s 1,300 1,470 90 10 -so 0 .05Pbo.o5) (Nam 1s) 03 1, 250 1, 420 150 8 -100 (Slo,9Pb0,l) (Nao.2sNbo,7s)0a 1, 200 1, 360 270 6 280 (Sru.sPbo.2) (NamsNboJa) 0a 1, 100 1, 300 310 7 650 o.ePbo.4) (Nama 130.1903 1, 000 1, 200 420 8 1, 000 (Ste ,5Pb0.5) (N a 25Nb0fl5) 03 900 1, 100 390 10 1, 600 o.u7Pbo.0a)( io zsNbo. 1, 280 1,440 80 10 40 msPboma) (LioasNbo )0: 1, 250 1, 380 130 8 50 (Sr Pbo 1) (L10,25N 0,75) a 1,200 1,340 250 8 50 (Sro, Pbo.2) (Llo,zsNbo,75) 0a 1, 100 1, 300 280 8 -10!) (Srn,sPbo .4) (Li0.2sNbo:1s) 0s 1, 000 1, 200 350 9 -350 o.sPbo.u) io,2aNbo.1a) a 900 1, 100 340 10 800 compositions are intimately mixed by a wet ball mill, dried, calcined for two hours at a temperature as shown at the column 2 of the tables (first firing temperature), pulverized, and pressed at a pressure of 700 kg. per cm.

into discs. The pressed discs are fired for two hours at 5 The embodiments of the invention in which exclusive property or privilege is claimed are defined as follows:

1. A sintered ceramic dielectric material consisting essentially of a perovskite-type compound of the chemical formula (Ba Pb (Na Nb )O wherein at ranges from 0.40 to 0.95.

2. A sintered ceramic dielectric material consisting essentially of a perovskite-type compound of the chemical I formula (Sr Pb (Na Nb )O wherein x ranges 0 from 0.50 to 0.97.

3. A sintered ceramic dielectric material consisting essentially of a perovskitc-type compound of the chemical TABLE 1 Power First Final Permitfactor Temperature firing firing tivity at at 20 C coeflioient of tempertemper- 20 C and 1 ermittivity Sample ature ature and 1 mHz p p m./ C number Composition C.) z (X10 11 Ba(Nao.25Nbo.-1) 0a 1, 300 1,550 85 13 ao.ta bn,oz)( an.2sNbo.1s)Oa 1,280 1, 450 100 12 18 (Bao,aPbo,7) (Nao.2sNbo,1s)Oa 800 950 300 20 5, 000

TABLE 2 Power First Final Permitfactor i firing firing tivity at at 20 C. Temperature temper temper- 20 C. and 1 coefiioient of ature ature and 1 mHz permittivity Composition 0. C.) mHz (X10 (p.p.m./ C.)

' msN 00,190: 1, 300 1,570 15 50 o.na bo.o2) (N 80,25Nb0fl5) 0a 1, 300 1, 500 12 70 29--.-.'.. (SI'o,4Pbo,o) (N an ,zsNboJfi) O3 850 1, 000 250 25 -2, 400

TABLE 3 Power First Final Permitfactor firing firing tivity 20 C. Temperature tempertemper- 20 and 1 coeflicient of Sample ature ature and 1 mHz permittivity number Composition 0.) O.) z (X10 (p.p.m.l C.)

10.2aNbn.7s)Oa 1, 300 1, 530 45 18 -30 32.. (Slo,qaPbo,oz) (L10,26Nb0,75)03 1, 280 1, 450 70 13 40 39 (Sr Pb (Lio,25Nbo,1s) 0a 850 1, 000 260 23 -1, 700

5 formula (Sr Pb )(Li Nb )O wherein x ranges from 0.50 to 0.97.

References Cited UNITED STATES PATENTS lllyn et a1 106-39 R Riley 317-258 Wainer 106-39 R Wainer 106-39 R Nitta et a1. 252-62.9

Kahn et a1. 106-39 R Lewis 106-39 R Goodman 106-39 R 6 FOREIGN PATENTS 1/ 1946 Great Britain 106-39 R OTHER REFERENCES 5 Evans, R. C.: An Introduction to Crystal Chemistry,

Cambridge (1964), pp. 166-171, 182-487, 200-201 Chemical Abstracts, 59:8348a, October 1963.

JAMES E. POER, Primary Examiner 10 W. R. SATIERFIELD, Assistant Examiner US. Cl. X.R. 

